A prisoner who is infatuated with Justin Bieber has threatened to castrate him with hedge clippers and strangle him.

Court documents in New Mexico revealed that killer Dana Martin persuaded a fellow prisoner and his relative to kill the singer, his bodyguards and two others. Two of the victims were to be castrated with hedge clippers.

The plot came into action when Dana became angry that Justin didn't respond to any of his letters.

"This perceived slight made Mr Martin upset and that, coupled with Mr Martin's perception of being a 'nobody' in prison, led him to begin plotting the kidnap and murder of Victim 3 (Justin)," court documents said.

Martin told investigators that Mark Staake and Tanner D Ruane headed from New Mexico to the East Coast, planning to be near a Bieber concert scheduled in New York City after killing and castrating two others. They missed a turn and crossed into Canada from Vermont.

The targets of the castration plot were not connected to Bieber, authorities said, and it did not appear that the pop singer was ever in immediate danger.

In a statement Justin's management said: "We take every precaution to protect and ensure the safety of Justin and his fans."

The Vermont-born prisoner is serving a life sentence for murdering a 15-year-old girl in 2000, and is currently being detained in Alberquerque.